I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
A 32-year-old man comes to the office because of a 2-week history of fever and throat pain. He is 173 cm (5 ft 8 in) tall and weighs 63 kg (140 lb); BMI is 21 kg/m2. His pulse is 110/min, respirations are 16/min, and blood pressure is 98/68 mm Hg. Physical examination shows scattered 2- to 4-cm lymph nodes in the neck, axillae, and inguinal regions. There is a bilateral tonsillar exudate but no ulcerations. Results of laboratory studies are shown:
Hemoglobin 9.6 g/dL
Hematocrit 29%
Leukocyte count 1500/mm3
Platelet count 60,000/mm3
A heterophile antibody test result is negative.
Which of the following is the most likely diagnosis?
(A) Epstein-Barr virus infection
(B) Gonococcal pharyngitis
(C) HIV infection
(D) Lymphogranuloma venereum infection
(E) Streptococcal pharyngitis
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Answer
The patient presents with fever, sore throat, lymphadenopathy, severe thrombocytopenia (platelet count 60,000/mm3), and leukopenia (leukocyte count 1500/mm3). The absence of heterophile antibodies suggests that infectious mononucleosis (choice A) is less likely.
The most likely diagnosis appears to be (C) HIV infection. HIV can present with acute symptoms resembling infectious mononucleosis, including fever, sore throat, and lymphadenopathy. Severe thrombocytopenia and leukopenia can occur in advanced HIV infection, particularly during acute retroviral syndrome. The negative heterophile antibody test further supports this possibility.
Other options are distraction as the clinical presentation and laboratory investigation support HIV infection.
The correct answer is (C) HIV infection
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